Bug in subresext

[Graham Herrick <pari@quadratic.com>]

Hi,

I'm using Pari 2.1.1 on MacOS X (the version distributed by fink).

I was doing some calculations and Pari said "*** bug in subresext, 
please report". This happens when inverting a polynomial modulo another 
polynomial when the coefficients (in Q) are fairly large.

One can reproduce this bug, at least on my machine, by reading in the 
data I've appended below. Sorry for the large size --- the bug doesn't 
seem to happen with polynomials with smaller coefficients.

For your info, the polynomial "ply" is the characteristic polynomial of 
the Hecke operator T_5 on cusp forms of weight 88, and the other 
polynomial is the first coefficient of a cuspidal eigenform. I'm trying 
to normalize this eigenvector, so need to invert the first coefficient. 
Everything works fine with the same calculations up to weight 86. In 
particular it works in weight 84, where the characteristic polynomial 
also has degree 7.

This happens with a stack size up to 512 MB. I set the debug level to 4 
and it didn't report any additional information. With the memory debug 
level at 4, it says

new bloc, size    119 (no 62): 002a362c
new bloc, size    969 (no 63): 002aa51c
  ***   bug in subresext, please report
killing bloc (no 62): 002a362c
killing bloc (no 63): 002aa51c

So it doesn't appear to be a memory problem (at least not an obvious 
memory problem).

Perhaps this has been fixed in subsequent releases? I did a quick search 
for subresext in the online version histories and didn't find anything.

Thanks for any help!

Regards,

Graham

p.s. You can also reply to herrick (at) math.northwestern.edu


ply = x^7 - 330373100841196567453715678850*x^6 - 
27454637116597781099764630240247455860681232063089728647387500*x^5 - 
12254614456003642941502499636378441724220623178074754159491805763418562754601397370765625000*
x^4 + 
174503643136586025133801567089728177325970177720892469125260754740570048019457296328670518649157335192195487351074218750000*
x^3 + 
83568693710880441319689349497913851727029023903525036233309796932775273553155429559779653474280692161321598199791214082364322092550897598266601562500000*
x^2 - 
295235265862672413714106315379535101098373504568690802922575008814432439084965547649824891831718081827345041623832782004960797901628522642774431341009437316097319126129150390625000000*
x - 
158754767573118537391494161435002861221639597086176783804946046471803893125111367620667569724098380364480393879032557338374348773330988358343388097186101605308690724434563134479958534939214587211608886718750000000;

eig = 
Mod
(4166081208812889384519028909184142067762531298862832978403782004273737426804509834241535300976644917647272048910752373018786743663229487796789174980187188792455460693155852576653061991347709007536213900669240479348969073472646477635873418672829015152504811348419864549613494886150971715783657290725195726524317948209763830116255108275768814717444554138670752863774843271828551831120342278574093663/
263934646670180220545619943389437693319334010446750517837952704102409755166075036350105179788653213683267871677906714302620799890834556572265281238408713676068335799465250085267299536105624323573940941159268698571101693275448960372464324708430346342810736352673879447292590870910712939224796004666194679434885333125838621101961079577363486902177892637166455037749059859889421698112520278988431383441663511097337826444094133442726425993648098451438975135359135968061252419006491540624220321950880354592179848973192915726862087753643195785767642827893621155128836152590755767055474218750000000000000000000000000000000*
x^6 - 
266055077570155898586727527228881069689711781126513934838388338312357850627072246941389246807786155373792777705692598345192172895092473543862996397977916183590157274320139836820827037666242927187971856218486489898530754560394851148004369521048105937417141032372290305599574041328069817001786378585307454431524798229754388374305403609505953881004458075523680693706258258227155795089114081792451492773196473418322975156173147/
20460050129471334926017049875150208784444496933856629289763775511814709702796514445744587580515752998702935788985016612606263557429035393198859010729357649307622930191104657772658878767877854540615576834051837098535014982592942664532118194451964832776026073850688329247487664411683173583317519741565479025960103343088265201702409269563061000168828886602050778120082159681350519233528703797552820421834380705219986546053808794009800464623883600886742258554971780469864528605154382994125606352781422836603089067689373312159851763848309750834700994410358229079754740510911299771742187500000000000000000000000000000*
x^5 - 
17894635403001334419942551596096279427918896037596154303833026272380287835902549858778036851781898406123499872165487094212923727930075991114659482001899692189844396125693162639062849541144217742690045672211295629971955395505151034745507235998591992612963069200830671935189432946928864369759765965925087889333281429093362849666967478509284818173774616014862266180812820096506020768587974917292823329759646926961855834993613663320936136342001967301388169/
41646492571231592985502160692613442732833768906785091572063543053634675371372786800805551051464017938188224327874826714417483217488687427576375737815970599774096378613846167300560084592603443561963067638543384389917426946816404003544666620659620724703863724287791628764116902707804803033498383379281211745149559467587948102873543128578064994426491934858612234753303330949021175244579136724012841568704301553820564330429054586623499170595360702396682467117812381548126614438894128698101825948856860685156583664409138576230704182034429315308503799273155211854648702578423000718812500000000000000000000000000000*
x^4 + 
49265843882020457266905937096483564520129420553545090150360979341651375378748277342307309378375309729762930326043314908511304495701857405797837214915164298940506261570089995676707578832800288329306710333325742504944808992205955314825490072235538376538967622699823440922083817115706478005173813702943621850471854791910014948130398147795935147593508336091427246435355858249179982044601172017479778246677913765473733202982372972924148870820332671451632055032154886483630667826188629/
1407651448907627842909973031410334364369781389049336095135747755212852027552400193867227625539483806310761982282169142947310932751117635052081499938179806272364457597148000454758930859229996392394351686182766392379209030802394455319809731778295180494990593880927357052227151311523802342532245358219704956986055110004472645877125757745938596811615427398221093534661652586076915723266774821271634045022205392519135074368502045027874271966123191741007867388582058496326679568034621549995841717071361891158292527857028883876597801352763710857427428415432646160687126147150697424295862500000000000000000000000000*
x^3 + 
100045400153897520095991599330893536467318741208780164102433873202813536700354550057018182315804188308701474814187667188500026359879969165716780064926449860869852033141694593216635397601872367345782490076296046633022947058181135528781959884672106839294955606132592912015746662514228935512124473611601939392791347117151883849633502785711246547443813619513455192021849035167915098638520693353837896983627176491536004380829780118183824518868820158461224240503015481770128914167688576000315276981382596472054299/
36035877092035272778495309604104559727866403559663004035475142533449011905341444963001027213810785441555506746423530059451159878428611457333286398417403040572530114486988811641828629996287907645295403166278819644907751188541298056187129133524356620671759203351740340537015073575009339968825481170424446898843010816114499734454419398296028078377354941394459994487338306203569042515629435424553831552568458048489857903833652352713581362332753708569801405147700697505962996941686311679893547957026864413652288713139939427240903714630750997950142167435075741713590429367057854061974080000000000000000000000*
x^2 - 
33717073322666861244381025694059067564530810062365439376723258241103787702763953798818346044595632122183791855277927091301126629237184595938646984786201180873118223344390626646549950867330033739724665259851462706222458924552523006324935013222761349897275088535478543063072905155752912201016768312812182044121832928929927403222416148050263269649938735963564138287715666680978095572290338241425289830227638094008641235608702581208932459089099906172076100433069091644995412450136987471437215808622210415598202211533176825006797903/
131788350508014711875639989409296675576197133018196129044023378408042100682391570150403756667650872471974424672634624217421384698253207615390304542783645405522395847266701939718687561129281490817080331579533968987091204346665318605484357974031932784171005086543507531106797983360034157600276045423266548658625868127504456171719019513768331258065755214242596551267980091258766784057159078124082583963678932291620051762591642889923954696531213562769559424540162550878950388815309939857896403957126818427071227293768921333909590727792460792503377069476848426838273570256668723426648064000000000000*
x - 
11618750746187199706732363084875153021461912056649131394487618975219222112944257449861338685915249888356259786239708043518348469186043172226070062422295738949534242392522499083552825373371738580589952567548792981524513209973625435590855104571543350243663756551971452376552711833222302471138506196350506226755275882965840252881084077198619980921837857744422165977355495359442565599414158589307208693593203539011066509730921123816733780628621849868956762684845753343049595013485914491062100537431695838637852003003339459234537541953363144560957762173/
2487581030787227003883047910693452456959002105265121403522210866172075780622469453161538190371880062881139370779315303200728072461037504113542338282220329866450384287577931544183153227583119752934382664284659617378458861769314032295225485076658049234859155919272842614808500183606912025487238166146081950717656939402111762577700939762189331027821812707546891585224177206432759205060477345604803059517183901688828258154725204042066905239593782272369195405145188057143690288421702827916791108794430637222505746522016137252044624981741564083381716481922447725021053197102834521454149632,
ply);

einv = Mod(1,ply)/eig;